Turbines, in particular gas turbines, are used in many fields to drive generators or production machines. The energy content of a fuel is used here to generate a rotational movement of a turbine shaft. To this end the fuel is combusted in a combustion chamber, during which process air compressed by an air compressor is supplied. The working medium produced in the combustion chamber by fuel combustion, which is at high pressure and has a high temperature, is guided by way of a turbine unit downstream of the combustion chamber, where it expands in a productive manner.
To generate the rotational movement of the turbine shaft a number of blades, generally combined in blade sets or rows of blades, are disposed on said turbine shaft, driving the turbine shaft by way of a pulse transfer from the working medium. Rows of vanes connected to the turbine housing are also generally disposed between adjacent rows of blades to guide the working medium in the turbine unit.
A turbine of this type comprises a plurality of elements or machine components, which are positioned appropriately in the turbine in compliance with predetermined dimensions, forms and/or tolerances. In many instances it may be desirable to minimize contact between adjacent machine components or elements, to keep wear of the relevant elements particularly low in such a manner. However during operation of the turbine it may be that actually undesirable contact between such elements occurs repeatedly due for example to thermal expansion or even to vibrations or the like produced during operation, so that a certain level of wear of such components results. Generally such machine components disposed adjacent to one another in the region of the combustion chamber of the gas turbine are for example what is known as a flame tube, a combined housing and an inner housing. Due to their structure these demonstrate such major deformation and critical tolerances that during operation of the gas turbine contact between said elements is unavoidable in places. Such contact produces undesirable and in particular possibly also critical wear over a long operating period, so said elements have to be inspected at regular intervals and be replaced/repaired as required.
In order to keep the level of wear of the relevant elements or machine components particularly low in such situations, the machine components can be produced in what is known as a plated design, whereby the regions particularly affected by the anticipated wear or contact with adjacent components are covered with a protective coating also referred to as plating. Such plating can be formed from an application material, which has a greater mechanical hardness and/or toughness than the base material of the respective component, so that wear occurring due to contact can be reduced by such an appropriate material selection. It is also possible to achieve greater corrosion resistance of the elements of the machine components by appropriate different chemical compositions of the base and/or application material.
The generally greater hardness and/or toughness of the application material for such purposes means that it is also more brittle than the respective base material of the base body of the machine component. Further processing of the base body equipped with the application material, for example by bending or the like, is therefore only possible to a limited extent.
Also cracks can form and other damage can occur in the region equipped with the application material during thermal expansion of the base body due to the different thermal expansion behavior. Machine components plated thus are therefore only conditionally suitable for use in regions with comparatively high thermal stress, for example in the interior of the combustion chamber of a gas turbine.
Since however the machine component should be equipped with appropriate plating so that it can essentially be used in compliance with wear-resistant working conditions and in order to avoid the possible disadvantages associated with plating, it is expedient to keep the lateral expansion of the plating as small as possible. In order still to be able to cover a sufficiently large partial region of the surface, individual zones of plating are embodied as decoupled from one another, in order thus to allow adequate yield in respect of thermal deformation and the like. This is achieved by embodying the plating in segments and forming it from a number of plating segments.
The plating segments can be applied to the base body of the machine component by means of appropriate techniques. However the plating segments are advantageously applied to the base body by hardfacing welding so that a particularly close connection to the base body is achieved and therefore a high level of stability of the machine component as a whole.
However for the segmented embodiment of the plating it is necessary to start and terminate the welding operation frequently, which can result in distortion of the base body due to the high working temperatures during hardfacing. Also in many instances cooling air is conducted around the outer region of the base body. The arrangement of the segments causes the cooling air to be injected into the hot gas path in the channels provided, with the result that hot and cold spots are produced corresponding to segmentation at the crossover points resulting from the segmentation preparations. Also a reduction in transverse stability and torsional rigidity of the rings forming the base body are associated with the segmentation of the plating elements in some circumstances.